ACCURACY OF NORTH-AMERICAN HUMAN SKELETON AGES

Accelerator mass spectrometry (AMS) radiocarbon dates fail to provide conclusive evidence that all New World human fossils are younger than approximately 11,000 yr. Because fossil bones vary widely in preservation, their radiocarbon dates are not equally accurate. Molecular-level radiocarbon dating, which used individual amino acids to assess fossil diagenesis, revealed that dates on known-age, noncollagenous bone were underestimated by at least 2000 to 9000 yr. The significance is that >11,000-yr-old fossil bones with poor preservation would yield Holocene and not Pleistocene radiocarbon ages, regardless of what chemical pretreatment or 14C counting method was used. Irreplaceable evidence for Pleistocene-age fossils in the New World could be lost if the diagenesis of fossil bones is not evaluated before the bones are radiocarbon dated. In contrast, radiocarbon ages for collagenous fossils can be determined more accurately if 14C is measured in several individual amino acids that are isolated from collagenous bone protein. Molecular-level radiocarbon dating will greatly improve not only the accuracy of chronologies for human migrations and animal extinctions, but of all late Quaternary chronologies that are based upon the 14C dating of fossil proteins. © 1990.